net: vrf: call netdev_lockdep_set_classes()

In case a qdisc is used on a vrf device, we need to use different
lockdep classes to avoid false positives.

Use the new netdev_lockdep_set_classes() generic helper.

Reported-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>